Variegated coatings

ABSTRACT

A PROCESS FOR PROVIDING COLOURED COATINGS VARIED IN COLOUR AND IN TEXTURE BY FORMING SURFACE FILM OXIDES, HAVING LIGHT INTERFERENCE COLOUR CHARACTERISTICS, OF TITANIUM MANGANESE, VANADIUM, COLUMBIUM, ZIRCONIUM, THORIUM OR MISCHMETAL ALLOYED WITH ZINC, TIN OR LEAD-TIN, SAID SURFACE FILM OXIDES HAVING A VARIED THICKNESS BY EXPOSING A MOLTEN STRATUM OF THE ALLOY TO A FREE OXYGEN CONTAINING GAS FOR REACTION OF OXYGEN WITH THE ALLOY AND CONTROLLING THE DEVELOPMENT OF OXIDE FILM THICKNESS.

United States Patent ice 3,684,586 VARIEGATED COATINGS Gerald Perley Lewis, Streetsville, Ontario, Robert William Smyth, Trail, British Columbia, Philip P. Booker, Beaconsfield, Quebec, and Richard Zeliznak, Oakville, Ontario, Canada, assiguors to Cominco Ltd., Montreal, Quebec, Canada No Drawing. Filed May 25, 1970, Ser. No. 40,421

Int. Cl. C23f 7/02 US. Cl. 1486.3 7 Claims ABSTRACT OF THE DISCLOSURE A process for providing coloured coatings varied in colour and in texture by forming surface film oxides, having light interference colour characteristics, of titanium, manganese, vanadium, columbium, zirconium, thorium or mischmetal alloyed with zinc, tin or lead-tin, said surface film oxides having a varied thickness by exposing a molten stratum of the alloy to a free oxygen containing gas for reaction of oxygen with the alloy and controlling the development of oxide film thickness.

This invention relates to a process for the formation of coloured and textured surfaces on zinc, tin and lead-tin alloys and is particularly directed to a process for the formation of variegated surfaces on zinc, tin and leadtin coatings and the novel compositions produced thereby.

A process for the production of coloured surfaces on zinc, tin and lead-tin coatings by the oxidation of a molten alloy of zinc, tin or lead-tin with a minor amount of an oxygen-avid additive such as titanium, manganese or vanadium by their exposure to a free-oxygen containing gas under controlled time and temperature conditions for the provision of a surface film of an oxide of the oxygenavid additive having light interference colour characteristics is taught in US. Pat. No. 3,530,013.

The process of the aforementioned patent is applicable to the formation of strata coatings on both non-metallic substrates such as graphite and on articles of various metals, such as iron, steel, copper, nickel and zinc. In this process, the zinc, tin or lead-tin alloy having the oxygen-avid additive alloyed therewith can be applied, for example, to the surface of the article to be coated by any suitable procedure but particularly elfective results are obtained by applying it by dipping the article into a melt of the alloy or by spraying or flowing the molten alloy onto the surface of the article.

The resulting coated surface is then contacted with a free oxygen-containing gas, such as air, with or without further heating, and then cooled to form a solid coating with a uniform and thin oxide surface film derived from the oxygen-avid additive and producing the desired light interference colour effects. The thickness of this oxide film and hence the final colour is dependent upon a number of factors such as the alloy composition, the alloy temperature and the period of time for which the coating is permitted to react with oxygen at elevated temperature. A detailed consideration of the effects of these several factors is given in the aforementioned patent.

Typical oxygen avid additives for use in the described process are titanium, manganese, vanadium, columbium, zirconium, thorium and mischmetal. Using zinc as the carrier metal, coloured coatings can also be obtained using as the additives cadmium, arsenic, copper, lead and chromium. Especially attractive surface coatings are obtainable by the use of titanium, manganese and vanadium with zinc as the carrier metal. The lead tin alloys which 7 can be used as the carrier metal are those alloys which contain at least by weight tin.

3,684,586 Patented Aug. 15, 1972 It will be understood that the term oxygen-avid element (or addition agent) refers to an element that forms a stable oxide film of suitable thickness for the production of light interference colour elfects. Elements such as sodium and potassium that will not form stable oxide films, and aluminum and magnesium that will not form a film of suitable thickness, do not provide discernible light interference colour elfects and are not included in this term for the operation of the process of the invention.

Uniformity of colour normally is provided by cooling the molten alloy to form an oxide film of constant thickness over the surface of the article.

We have found that the coloured coatings can be varied in colour and in texture by variation of the oxide film thickness formed on the metal alloy and by variation of the thickness of the coating or the article surface contours respectively. Gradual variation of the thickness of the oxide film over areas of the metal alloy provides multi-coloured mottled or streaked effects i.e. various colours graduating into each other, whereas abrupt variation of the thickness of the oxide film provides sharply defined colour changes. Variation of the thickness of the metal alloy coating or the surface configuration of the article coated can be utilized to provide attractive surface textures.

The term variegated used herein in the description of the method and product of the invention and in the appended claims will be understood to means varied in colour or varied in colour and texture.

The oxide film thickness can be regulated by a number of techniques. Abrupt and sharply-defined colour changes can be obtained by rupturing first-formed partially developed oxide films to expose fresh molten material which, when exposed to a free oxygen containing gas, develops a new oxide film which has a final oxide film thickness less than that of the adjacent first-formed oxide films. Partially developed oxide films can be broken by tapping or by jarring the coated article while the metal alloy is molten such that fresh surfaces of the molten alloy are exposed to the oxygen containing gas for oxidation. Since the total time of exposure of the newly exposed alloy will be less than that of the alloy originally exposed, the newly exposed metal will have a thinner oxide film and a resulting colour lower on the colour sequence as shown in Patent 3,530,013.

Oxide film thickness also can. be controlled by regulating the availability of oxygen-acid additive during solidification of the molten alloy such that localized deficiences of the additive occur during oxide film development thereby locally arresting said oxide film develop ment. For example, the alloy thickness can be controlled across the molten alloy stratum to form thick and thin zones which, when oxidized in the molten state for a sufficient length of time, depletes the additive present in the thin zones of the stratum thereby arresting oxide film development, and local colour, while permitting continuation of oxide film development in thick zones still having available additive for the production of a colour higher in the colour sequence.

Variations in thickness of the molten alloy stratum can be controlled by inclining the article surface to the horizontal thereby causing the molten alloy to fiow across the article surface to form a drainage pattern, i.e. a series of undulations. The drainage pattern assumed by the molten alloy is largely determined by the nature of the substrate surface, i.e. the degree of roughness, and, for example, the presence of protuberances such as produced by an 0 embossed surface will provide a distinctive flow pattern The availability of oxygen-avid additive present in the alloy can be further controlled by adding a minimum amount of additive to the host metal which will provide the order of colour desired under the coating conditions involved as set forth in our aforementioned Patent 3,530,- 013. The presence of a minimum amount of additive coupled with a variation of thickness of the alloy coating and a variation in cooling rate is effective in providing a multi-coloured mottled or streaked effect.

The rate of cooling of the molten alloy will be influenced locally by the nature of the article surface and by the variations in thickness of the molten alloy to affect oxide film development. The presence of perforations or the like openings in the article coated will further influence the cooling rate of the molten alloy.

Post-heating selectively of the alloy surface, such as by induction heating, can be utilized to control local development of the thickness of oxide film to form desired patterns and to achieve desired colours. Also, selective cooling of the molten stratum to arrest or impede oxide film development can be utilized for selective colour attainment as desired.

The method of the invention will now be described with reference to the following examples, it being understood that although the following description relates to binary alloys of zinc with titanium and vanadium, binary alloys of zinc with manganese, columbium, zirconium, thorium and mischmetal, and alloys of said additives with tin and lead-tin, said lead-tin alloys containing at least tin, are also within the scope of the invention.

EXAMPLE 1 A 24-gauge steel sheet panel coated in a zinc-0.1% vanadium bath at 500 C. normally producing a first order blue colour produced, on jarring of the sheet sufliciently to rupture the partially developed oxide film before solidification of the zinc alloy, a variety of red and gold bands randomly dispersed the blue matrix when the oxide film stabilized. The colours produced and intensity of film cracks could be varied by controlling the severity of jarring and the time the coating remained molten after withdrawal from the bath.

EXAMPLE 2 A panel of embossed -gauge steel sheet having uniformly spaced depressions was immersed in a zinc-0.1% vanadium bath at 460 C. The resulting coating had thick and thick zones produced by undulations formed by the drainage pattern as the sheet was inclined to the horizontal and a variety of gold and bronze colours provided. The variation in colour was a combined effect of various cooling rates of the embossed substrate surface and various cooling rates of the thick and thin regions of accumulated molten alloy.

EXAMPLE 3 A panel of 20-gauge steel sheet was dipped in a zinc- 0.08% titanium bath at 660 C. and permitted to drain as the sheet was inclined to the horizontal. This test produced a heavily streaked coloured surface, the primary matrix colour being second-order green with streaks of blues, reds and yellows. The streaking was believed to be associated with the lack of sufficient titanium for oxidation of the said additive to a uniform thickness across the sheet surface. Increasing the titanium content in the zinc to 0.12% eliminated the streaking effect and produced a consistently green coloured panel.

EXAMPLE 4 A panel of 20-gauge steel sheet perforated with uniformly spaced /2 inch diameter holes was dipped in a zinc-0.1% vanadium bath maintained at 500 C. The panel upon cooling consisted primarily of a blue colour having a lower order red colour about the perforations where a more rapid cooling took place to arrest the oxide film development.

We claim:

1. A method of forming a variegated surface on a zinc, tin or lead-tin alloy which comprises: melting an alloy of said metal and an oxygen-avid additive selected from the group consisting of titanium, manganese, vanadium, columbium, zirconium, thorium and mischmetal; forming a stratum of said molten alloy; exposing said molten stratum to a free oxygen containing gas for the provision thereon of a surface film of an oxide of the said additive having light interference colour characteristics, and varying the thickness of the oxide film over areas of said alloys as the film is formed on the stratum by permitting a first oxide film to partially develop and then rupturing the partially developed oxide film to expose fresh molten alloy to the free oxygen containing gas to permit a second oxide film to form whereby the first-formed oxide film develops to a greater thickness than the second-formed oxide film.

2. A method as claimed in claim 1 in which said stratum comprises an adherent coating of said alloy on an article surface.

3. In a method as claimed in claim 2, varying the oxide film thickness formed on the stratum by controlling the availability of oxygen-avid additive such that localized deficiencies of the additive occur during oxide film development thereby locally arresting oxide film development by varying the alloy thickness across the stratum to form thick and thin zones and oxidizing the alloy in its molten state sufficiently to deplete the additive in thin zones on the stratum.

4. In a method as claimed in claim 3, varying the molten alloy thickness on the article surface by the configuration of the article.

5. In a method as claimed in claim 3, varying the alloy thickness by flowing the molten zinc alloy across the article surface to form a drainage pattern.

6. In a method as claimed in claim 5, determining the drainage pattern by use of asubstrate surface of the desired nature.

7. In a method as claimed in claim 3, controlling the availability of oxygen-avid additive using an alloy with a minimum amount of additive necessary for the order of colour desired.

References Cited UNITED STATES PATENTS 3,530,013 9/1970 Smyth et a1. l486.3 2,059,053 10/1936 Stareck 1486.35

OTHER REFERENCES Fishlock: Metal Colouring, Robert Draper Ltd., 1962. pp. 14, 15.

RALPH S. KENDALL, Primary Examiner U.S. Cl. X.R. 117-131 

